What causes these are beyond me. Here goes:If one day your graphics look all fuzzy and torn and when you try to reboot your monitor won't come on or your OS refuses to respond, and even if it does you lose all sounds on Windows. Then this is what to do. Turn off all power and open up your CPU and gently remove your graphics and sound card. If it's all dusty inside now is a good time to clean up. Replace the cards and reboot. Your system will detect your cards as new installations and voila!
This is all from personal experience. I'll post some more personal tips as soon as that brick hit me on the head again.
I'm surrounded by grumpy old men!